An animal model of human syphilis has been developed, where inbred Syrian hamsters infected with Treponema pallidum develop lesions like "hard chancre" at the site of inoculation (inguinal area) which eventually heal, then animals develop oral ulcers corresponding to mucosal lesions of human secondary syphilis. The proposed research will examine the underlying cellular mechanisms of immunosuppression associated with acute and chronic syphilitic infection. Specific B lymphocyte, T lymphocyte and macrophage cell functions will be assessed in hamsters at various stages of infection. Conclusions will be made concerning the level of immunosuppression (i.e., whether B, T, or macrophage cells are affected), the nature of immunosuppression (i.e., whether it is passive or active) and the cause(s) of immunosuppression (development of treponema specific suppressor T cells or antiidiotypic antibodies and/or non-cytophilic or non-opsonizing antibodies). Elucidation of the specific cellular mechanisms involved in the development of secondary and tertiary syphilis may ultimately enable researchers to correct the deficiencies by immunotherapeutic means.